It is known in the prior art to carry out chemical reactions, in particular for refining petroleum fractions or hydrocarbons, in catalytic reactors that use a granular bed. Generally, catalyst grains of a characteristic size between 0.5 and 5 mm are used. These catalyst grains often have an essentially spherical shape to facilitate their flow. They can, however, have another shape, for example if they are produced by extrusion. The catalysts that are used in the reactor according to the invention are all catalysts that have a characteristic size (for example, a diameter) of between 0.5 and 5 mm in diameter, and preferably between 1 to 4 mm.
In general, the deactivation of catalysts, and, for example, that of catalysts that comprise a zeolite used for the purpose of the production of diesel fractions by oligomerization, is fast. It is therefore necessary to initiate a replacement of the catalyst regularly so as to maintain the performance levels of the reactor in terms of selectivity and output.
Two types of technology are commonly used for this purpose:
In the “fixed-bed” technology, all of the catalyst that is contained in the reactor at the end of a cycle is changed when the consumption of the catalyst is considered to be spent. The operation is then typically cut off, the reactor is emptied, and then it is filled again by the new and/or regenerated catalyst.
Another type of technology is used for catalytic reactions with circulation (continuous or semi-continuous) and regeneration (continuous or semi-continuous) of the catalyst: that of the “moving bed” that consists of a stack of catalyst grains contained in the reactor, as in a fixed bed, but said grains moving (at a very slow average speed, continuously or intermittently) from the top to the bottom of the reactor under the effect of the force of gravity. At the bottom of the reactor, a small amount of spent catalyst is drawn off continuously or intermittently, and the same amount of new catalyst and/or regenerated catalyst is introduced at the top of the reactor. It is possible, for example, to draw off and to reintroduce a suitable amount of catalyst every 4 or 8 hours such that the overall activity of the catalyst remains constant. The spent catalyst that is drawn off is typically regenerated and then recycled, optionally except for a small amount of catalyst that is eliminated and replaced by new catalyst.
The reactor according to the invention can be used both in a fixed bed and in a moving bed, this second variant of implementation representing, however, the preferred variant.
Furthermore, for the reactions with strong endothermicity or with strong exothermicity, means for heat exchange with the reaction fluid (furnace or heat exchanger) are sometimes used inside or outside the reactor so as to maintain the temperature difference between the inlet and the outlet of the reactor within desired limits and/or to reset the temperature of the reaction fluid between two or more reactors that are arranged in a series.
Patent US 2002/0011428 A1 describes a multi-staged moving-bed reactor that is intended to implement hydrotreatment reactions. One system, subject of other patents (in particular patent U.S. Pat. No. 5,076,908), makes it possible to add and to withdraw catalyst continuously or semi-continuously from each stage of the reactor. The feedstock flows from one stage to the next. By contrast, the catalyst of one stage does not flow into the next stage. It was found that such a system can also be used to implement an oligomerization reaction. The described system, however, does not make it possible to effectively monitor the temperature profile within each reaction section.
Patent WO 02/04575 describes a process for oligomerization on a zeolite implementing a tubular-type reactor, in a fixed bed, or any other reactor that can be used so as to carry out the oligomerization reaction. The patent describes a method that makes it possible to add and to withdraw the catalyst continuously or semi-continuously from the reactor. By contrast, the problem of monitoring the exothermicity of the reaction is not addressed.
Patent EP 1236506A1 describes a multi-staged reactor with a small bed thickness with an internal heat exchanger, used primarily within the framework of reactions for dehydrogenating long paraffins. This system makes it possible to monitor specifically the temperature within each reaction section. In contrast, it is hardly suitable for implementing large amounts of catalyst, being suitable for small bed thicknesses. The catalyst filling rate in the reactor is very low here.
The above-mentioned patent applications that describe superposed or multi-staged reactors therefore do not describe means that make it possible both to use large amounts of catalyst and to implement integrated thermal means.
This invention describes a reactor and a process for chemical conversion of hydrocarbons that uses this reactor, making it possible to optimally resolve the problems that are linked to the implementation of strongly exothermic or endothermic reactions, in particular oligomerization reactions. It makes it possible to implement a compact reactor, having a large capacity for what the amount of catalyst present is and having, moreover, an inside volume that is noteworthy for the integration of a heat exchanger.